JP7327110B2 - DC-DC converter - Google Patents

Description

The present invention relates to a DC-DC converter composed of a synchronous rectification SEPIC circuit.

A buck-boost DC-DC converter is used as means for generating a stable output voltage from an unstable input power source such as an automobile battery. In such a DC-DC converter, high efficiency is required in order to suppress wasteful consumption of the battery. Therefore, there has been proposed a DC-DC converter composed of a synchronous rectification SEPIC circuit that achieves loss reduction by using a P-channel MOSFET as a rectifying means (see, for example, Patent Document 1).

Referring to FIG. 10, the DC-DC converter 100 shown in Patent Document 1 includes an input side inductor L1, a coupling capacitor Cc, and an output side inductor connected between the input DC power source Vi and ground. L2, a synchronous rectifying element Q2 connected between the connection between the coupling capacitor Cc and the output inductor L2 and the output terminal Vo, and the connection between the input inductor L1 and the coupling capacitor Cc and the ground. It is composed of a synchronous rectification SEPIC circuit having a switching element Q1 connected therebetween.

When performing the step-up/step-down operation, the control circuit 101 turns on the synchronous rectification element Q2 when the current flows through the output capacitor Co, thereby reducing the loss due to the forward resistance. Then, the control circuit 101 detects the end timing of the regeneration period from the change in the total current of the current IL1 flowing through the inductor _L1 and the current IL2 flowing through the inductor _L2 , thereby turning off the synchronous rectifier element Q2 and reducing the current. This prevents backflow and loss.

JP 2014-17930 A

However, in the prior art, the end timing of the regeneration period is detected from the change in the total current of the current IL1 flowing through the inductor _L1 and the current _IL2 flowing through the inductor L2. There was a problem that the current detection resistor had to be connected in series, which greatly increased the loss.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a DC-DC converter capable of detecting the end timing of a regeneration period with a simple configuration.

The DC-DC converter of the present invention comprises an input inductor connected between an input DC power supply and a first terminal of a coupling capacitor, and an output connected between a second terminal of the coupling capacitor and ground. a side inductor, a switching element connected between the first terminal of the coupling capacitor and the ground, and a synchronous rectification element connected between the second terminal of the coupling capacitor and an output terminal. , wherein the inductances of the input side inductor and the output side inductor are set to the same value, and the input side inductor and the output side inductor a zero current detection unit that detects the end of flowing regenerative current and outputs a zero current detection signal; , an output control unit for controlling off the synchronous rectification element, wherein the input side inductor or the output side inductor is used as a detection inductor, the zero current detection unit is provided in parallel with the detection inductor, The zero-current indirect detection unit detects the end of the regenerative current flowing through the detection inductor by indirectly detecting the voltage generated across the DC resistance component of the detection inductor.

According to the present invention, since the inductances of the input side inductor La and the output side inductor Lb are set to the same value, the end timing of the regeneration period can be detected with a simple configuration.

1 is a diagram showing the configuration of a first embodiment of a DC-DC converter according to the present invention; FIG. 2 is an operation waveform diagram of the PWM signal generator shown in FIG. 1; FIG. 2 is an operation waveform diagram of the DC-DC converter shown in FIG. 1; FIG. FIG. 2 is a diagram showing the configuration of a second embodiment of a DC-DC converter according to the present invention; 5 is a diagram showing a configuration of a zero-current indirect detection unit shown in FIG. 4; FIG. FIG. 5 is an operation waveform diagram of the DC-DC converter shown in FIG. 4; FIG. 5 is a diagram showing the configuration of a DC-DC converter according to a third embodiment of the present invention; FIG. 8 is an operation waveform diagram for explaining the relationship between the output load current and the zero current detection period shown in FIG. 7; 8 is an operation waveform diagram of the DC-DC converter shown in FIG. 7; FIG. 1 is a diagram showing a configuration of a conventional DC-DC converter; FIG.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the present embodiment described below does not unduly limit the content of the present invention described in the claims, and all of the configurations described in the present embodiment are essential as means for solving the present invention. not necessarily.

(First embodiment)
Referring to FIG. 1, the DC-DC converter 10 of the first embodiment includes an input side inductor La, an output side inductor Lb whose inductance is set to the same value as the input side inductor La, and a coupling capacitor Cc. , a switching element Q1 composed of an N-channel MOSFET, a synchronous rectification element Q2 composed of a P-channel MOSFET, a driver D1 of the switching element Q1, a driver D2 of the synchronous rectification element Q2, an output capacitor Co, and an output load Ro, a current sensor A1, an AD converter 11, a subtractor 12, a filter calculator 13, a PWM signal generator 14, a zero current detector 15, and a PWM output controller 16.

In general, an error of about ±20% is allowed for the inductance of the inductor. Therefore, although it is preferable that the inductance of the input side inductor La and the inductance of the output side inductor Lb are completely the same value, they actually include a predetermined error. In order to reduce the inductance error, it is preferable to use an element in which the input side inductor La and the output side inductor Lb are made of a single core material. Also, even if the input side inductor La and the output side inductor Lb of the same production lot are used, the error can be reduced.

Input side inductor La, coupling capacitor Cc, and output side inductor Lb are connected in series between input DC power source Vi and ground. That is, the input side inductor La is connected between the input DC power source Vi and the first terminal of the coupling capacitor Cc.
The output-side inductor Lb is connected between the second terminal of the coupling capacitor Cc and the ground.

The switching element Q1 is connected between the connection between the input inductor La and the coupling capacitor Cc and the ground, and the synchronous rectification element Q2 is connected between the connection between the coupling capacitor Cc and the output inductor Lb and the output terminal Vo. , and the DC-DC converter 10 is composed of a synchronous rectification SEPIC circuit.

Energy is excited to the input side inductor La and the output side inductor Lb while the switching element Q1 is on, and the excited energy is transferred to the output capacitor while the switching element Q1 is off and the synchronous rectification element Q2 is on. An output voltage Vo is generated by supplying Co and an output load Ro.

The AD converter 11 detects the output voltage Vo, converts it into a digital value with a predetermined number of bits, and outputs the digital conversion value to the subtractor 12 . The subtractor 12 generates a difference value between the output target value and the digital conversion value and outputs it to the filter calculation section 13 . The filter calculator 13 performs PI and PID calculations based on the difference value and outputs the calculated values to the PWM signal generator 14 .

The PWM signal generator 14 is composed of a digital circuit. Referring to FIG. 2, by comparing the PWM count value and the calculated value, the first PWM signal having the DUTY corresponding to the calculated value and the first PWM signal are inverted. A second PWM signal having a complementary waveform is generated.

The PWM count value is limited by the PWM count maximum value, and the PWM signal generator 14 clears the PWM counter when the count value reaches the maximum value. By repeating this, a first PWM signal and a second PWM signal having a predetermined frequency are generated and output.

The first PWM signal is a signal for on/off controlling the switching element Q1. When the PWM count value reaches the calculated value, it switches from HIGH to LOW. It switches to HIGH. The second PWM signal is a signal for on/off controlling the synchronous rectification element Q2. When the count value reaches the maximum value, the second PWM signal switches from HIGH to LOW. to HIGH.

The current sensor A1 is composed of a current detection resistor and a Hall element, directly detects the current flowing between the ground and the output side inductor Lb as an inductor current I Lb, and outputs the inductor current _ILb to the zero current detection unit 15 .

Referring to FIG. 3, when the first PWM signal switches from LOW to HIGH at time t1, the switching element Q1 switches from off to on via the driver D1. At this time, a combined current of the inductor current _ILa and the inductor current _ILb flows between the drain and source of the switching element Q1 via the coupling capacitor Cc to excite the input side inductor La and the output side inductor Lb. do. Note that the dead time Td is omitted in FIG. 3 for simplification.

When the first PWM signal switches from HIGH to LOW at time t2, the switching element Q1 switches from ON to OFF via the driver D1. On the other hand, when the second PWM signal switches from LOW to HIGH, the synchronous rectifier Q2 switches from off to on via the PWM output control section 16 and the driver D2. As a result, the energy excited by the input side inductor La and the output side inductor Lb is supplied to the output capacitor Co and the output load Ro.

Here, in the first embodiment, the input side inductor La and the output side inductor Lb are set to have the same inductance value. As a result, at time t3 when the inductor current _ILb becomes zero, the inductor current _ILa also becomes zero, and the regeneration of the input side inductor La and the output side inductor Lb is completed almost at the same time. That is, the timing at which the inductor current _ILb becomes zero coincides with the end timing of the regeneration period of the input side inductor La and the output side inductor Lb.

The zero current detector 15 outputs to the PWM output controller 16 a zero current detection signal that notifies the timing at which the inductor current _ILb detected by the current sensor A1 becomes zero. In the first embodiment, the zero current detector 15 outputs to the PWM output controller 16 a zero current detection signal that switches from HIGH to LOW at the timing when the inductor current _ILb becomes zero.

Based on the zero current detection signal, the PWM output control unit 16 outputs a second PWM control signal for turning off the synchronous rectifier element Q2 through the driver D2 at the timing when the inductor current _ILb becomes zero. In the first embodiment, the PWM output control section 16 outputs the second PWM control signal obtained by ANDing the second PWM signal and the zero voltage detection signal. Accordingly, when the zero current detection signal switches from HIGH to LOW, the second PWM control signal switches from HIGH to LOW, and the synchronous rectifier Q2 is forcibly turned off.

After time t4, by repeating the operation from time t1 to time t3, it is possible to detect the end timing of the regeneration period of the input side inductor La and the output side inductor Lb from the current change at one point. power supply can be configured.

In the first embodiment, in order to accurately detect changes in the inductor current _ILb , the current sensor A1 is provided between the ground and the output side inductor Lb to directly detect the inductor current _ILb with reference to the ground. configured as On the other hand, when not adhering to ground-based detection, any one of the current sensors B1 to B5 indicated by the dashed line in FIG. 1 is provided instead of the current sensor A1, and the The timing at which the current becomes zero may be detected as the end timing of the regeneration period.

(Second embodiment)
Referring to FIG. 4, the DC-DC converter 20 of the second embodiment replaces the current sensor A1, the PWM signal generator 14 and the zero current detector 15 of the DC-DC converter 10 with the PWM signal generator 14a. and a zero-current indirect detector 21 are provided. In FIG. 4, the resistor Rdcr connected in series with the output side inductor Lb is the DC resistance component of the output side inductor Lb, and the output side inductor Lb is equivalently an LR circuit to which the resistor Rdcr is added. can be regarded as

Referring to FIG. 5, the zero current indirect detection unit 21 is composed of a resistor R1, a sense capacitor C1, a comparator Comp1, and an SR flip-flop FF1. The resistor R1 and the sense capacitor C1 are connected in series to form an RC circuit, and are connected in parallel with the output side inductor Lb. One end of the resistor R1 is connected to the connection point between the output inductor Lb and the synchronous rectifier Q2, the other end of the resistor R1 is connected to one end of the sense capacitor C1, and the other end of the sense capacitor C1 is grounded. It is

Here, the resistance value R of the resistor R1 and the capacitance C of the sense capacitor C1 are as follows, where L is the inductance of the output side inductor Lb, and Rdcr is the resistance value of the DC resistance component of the output side inductor Lb.
C×R=L÷Rdcr
is set to satisfy the relationship of

As a result, a signal similar to the signal generated across the resistor Rdcr, which is the DC resistance component of the output inductor Lb, is generated in the voltage VC across the sense capacitor C1. If the voltage generated across the resistor Rdcr, which is the DC resistance component of the output side inductor Lb, can be detected, the regeneration end timing of the output side inductor Lb can be easily detected. can't. Therefore, the regeneration completion timing of the output side inductor Lb is indirectly detected by detecting the voltage VC across the sense capacitor C1, which is similar to the voltage generated across the resistor Rdcr, by the comparator Comp1.

The comparator Comp1 has a non-inverting input terminal connected to the connection point between the resistor R1 and the sense capacitor C1, an inverting input terminal connected to the ground, and an output terminal connected to the set terminal of the SR flip-flop FF1.

The PWM signal generator 14a is input to the reset terminal of the SR flip-flop FF1, and the output from the inverted output terminal of the SR flip-flop FF1 becomes the zero current detection signal supplied to the PWM output controller 16.

Referring to FIG. 6, when the first PWM signal switches from LOW to HIGH at time t1, the switching element Q1 switches from OFF to ON via the driver D1. At this time, a combined current of the inductor current _ILa and the inductor current _ILb flows between the drain and source of the switching element Q1 via the coupling capacitor Cc to excite the input side inductor La and the output side inductor Lb. do. At this time, -Vi is generated in the voltage VL of the output side inductor Lb, thereby charging the voltage VC across the sense capacitor C1 in the zero current indirect detection section 21 to the negative voltage side. Note that the dead time Td is omitted in FIG. 3 for simplification.

When the first PWM signal switches from HIGH to LOW at time t2, the switching element Q1 switches from ON to OFF via the driver D1. On the other hand, when the second PWM signal switches from LOW to HIGH, the synchronous rectifier Q2 switches from off to on via the PWM output control section 16 and driver D2. As a result, the energy excited by the input side inductor La and the output side inductor Lb is supplied to the output capacitor Co and the output load Ro. At this time, Vo is generated in the voltage VL of the output side inductor Lb, whereby the voltage VC across the sense capacitor C1 in the zero current indirect detection section 21 is discharged.

Here, also in the second embodiment, the inductances of the input side inductor La and the output side inductor Lb are set to the same value. As a result, at time t3 when the inductor current I _Lb becomes zero, the inductor current I _La also becomes zero, the regeneration of the input inductor La and the output inductor Lb is completed almost at the same time, and the voltage across the sense capacitor C1 is VC reaches zero volts. That is, the timing at which the inductor current _ILb becomes zero coincides with the end timing of the regeneration period of the input side inductor La and the output side inductor Lb.

When the voltage VC across the sense capacitor C1 reaches zero volts, the output of the comparator Comp1 switches from LOW to HIGH, and the SR flip-flop FF1 is set. For this reason, the zero current detection signal switches from HIGH to LOW.

Based on the zero current detection signal, the PWM output control unit 16 outputs a second PWM control signal for turning off the synchronous rectifier element Q2 through the driver D2 at the timing when the inductor current _ILb becomes zero. In the second embodiment, the PWM output controller 16 outputs a second PWM control signal obtained by ANDing the second PWM signal and the zero voltage detection signal. Accordingly, when the zero current detection signal switches from HIGH to LOW, the second PWM control signal switches from HIGH to LOW, and the synchronous rectifier Q2 is forcibly turned off.

In addition to the functions of the first embodiment, the PWM signal generator 14a outputs a reset signal to the zero current indirect detector 21 when the count value reaches the maximum value. When the reset signal is output to the zero-current indirect detection unit 21 at time t4 when the second PWM signal switches from HIGH to LOW, the SR flip-flop FF1 is reset and the zero-current detection signal switches from LOW to HIGH.

By repeating the operation from time t1 to t4, it is possible to detect the end timing of the regeneration period of the input side inductor La and the output side inductor Lb from the current change detected at one point without using the current detection resistor. A highly efficient power supply can be configured with a simple configuration.

In the second embodiment, the zero current indirect detection unit 21 detects the timing when the inductor current I _Lb of the output side inductor Lb becomes zero. A certain effect can also be obtained by detecting the timing at which the inductor current _ILa of the input side inductor La becomes zero.

(Third Embodiment)
Referring to FIG. 7, the DC-DC converter 30 of the third embodiment is provided with a zero current period measuring section 31 in addition to the configuration of the DC-DC converter 20 .

The zero-current period measuring unit 31 defines the period from the completion of regeneration of the output-side inductor Lb to the start of the next cycle, that is, the period in which the synchronous rectifier Q2 is turned off by the zero-current detection signal as the zero-current period Tz. The counter maximum value of the PWM signal generator 14 is controlled according to the zero current period Tz. The zero-current period measuring unit 31 sets the counter maximum value to a smaller value as the zero-current period Tz becomes shorter, and sets the counter maximum value to a larger value as the zero-current period Tz becomes longer.

Referring to FIG. 8, when the switching period Ts of the first PWM signal and the second PWM signal is constant at Ts0, when the value of the output load current Io of the output load Ro decreases, the ON DUTY of the switching element Q1 decreases. Therefore, the zero current period Tz becomes longer from Tz0 to Tz1 shown in FIG. 8 as the value of the output load current Io of the output load Ro becomes smaller.

Therefore, as shown in FIG. 9, the zero-current period measuring unit 31 extends the switching period Ts by setting the counter maximum value to a larger value as the zero-current period Tz becomes longer. When the maximum counter value of the PWM signal generator 14 changes, the ON DUTY of the switching element Q1 spreads through the AD converter 11, the subtractor 12, and the filter calculator 13 so as to keep the output voltage Vo constant. Since feedback control is performed, the zero current period Tz2 and the switching period Ts1 converge to constant values.

As a result, the lighter the load, the lower the switching frequency, thereby reducing the switching loss and improving the light-load efficiency more than in the second embodiment.

Further, it is preferable to prevent the switching frequency from dropping to an audible frequency (20 kHz or less) by setting an upper limit to the maximum counter value of the PWM signal generation unit 14 . As a result, it is possible to prevent the output capacitor Co from generating noise.

As described above, in the present embodiment, the input side inductor La connected between the input DC power supply Vi and the first terminal of the coupling capacitor Cc, the second terminal of the coupling capacitor Cc and the ground are connected. A switching element Q1 connected between the first terminal of the coupling capacitor Cc and the ground, and a second terminal of the coupling capacitor Cc and the output terminal Vo. A DC-DC converter 10 configured by a synchronous rectification SEPIC circuit including a synchronous rectification element Q2 and a synchronous rectification element Q2, wherein the inductances of the input side inductor La and the output side inductor Lb are set to the same value, and the input side inductor A zero current detection unit 15 that detects the end of the regenerative current flowing through La and the output side inductor Lb and outputs a zero current detection signal; and a PWM output control section 16 for controlling the synchronous rectifier Q2 to be off until the cycle Ts is started.
With this configuration, the inductances of the input side inductor La and the output side inductor Lb are set to the same value, so the end timing of the regeneration period can be detected with a simple configuration. That is, since the end timing of the regeneration period can be detected from the current change at one point, the elements required for current detection can be reduced, and the loss can be greatly reduced.

Further, in the present embodiment, between the input side inductor La and the first terminal of the coupling capacitor Cc, between the output side inductor Lb and the ground, and between the second terminal of the coupling capacitor Cc and the synchronous rectification element Q2. or between the synchronous rectifier Q2 and the output terminal Vo. The end of the regenerative current flowing through the input side inductor La and the output side inductor Lb is detected using only the detection result of one of the current sensors A1, B1 to B5.

Further, in the present embodiment, the DC-DC converter 20 is provided in parallel with the output side inductor Lb (or the input side inductor La) as a detection inductor, and the DC resistance component of the output side inductor Lb A zero-current indirect detection unit 21 is provided to detect the end of the regenerative current flowing through the output-side inductor Lb by indirectly detecting the generated voltage.
With this configuration, the regeneration end timing of the output-side inductor Lb is indirectly detected from the amplitude and DUTY ratio of the AC voltage generated in the output-side inductor Lb, so no loss occurs and higher efficiency can be achieved.

Further, in the present embodiment, the zero-current indirect detection unit 21 includes an RC circuit including a resistor R1 and a sense capacitor C1 connected in parallel with the output inductor Lb. is set to be equal to the value obtained by dividing the inductance L of the output side inductor Lb by the resistance value Rdcr of the DC resistance component of the output side inductor Lb. The end of the regenerative current flowing through the output side inductor Lb is detected.
With this configuration, a signal similar to the signal generated across the resistor Rdcr, which is the DC resistance component of the output inductor Lb, can be generated in the voltage VC across the sense capacitor C1.

Further, in the present embodiment, the DC-DC converter 30 measures the zero current period Tz during which the PWM output control unit 16 turns off the synchronous rectifier element Q2. and a zero-current period measuring unit 31 that lowers the switching frequency of the synchronous rectifier Q2.
With this configuration, the regeneration end timing of the output side inductor Lb is indirectly detected from the amplitude and DUTY ratio of the AC voltage generated in the output side inductor Lb, and the period from the end of regeneration to the start of the next cycle is measured. By controlling the switching frequency according to this period and controlling the switching frequency to be lower as the load becomes lighter, the light load efficiency can be improved.

Although the embodiments and examples of the present invention have been described in detail as described above, it should be understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present invention. , will be easily understood. Accordingly, all such modifications are intended to be included within the scope of the present invention. For example, a term described at least once in the specification or drawings together with a different, broader or synonymous term can be replaced with the different term anywhere in the specification or drawings. Further, the configurations and operations of the power supply device and the power transmission coil are not limited to those described in the embodiments and examples of the present invention, and various modifications are possible.

10, 20, 30 DC-DC converter 11 AD converter 12 subtractor 13 filter operation unit 14, 14a PWM signal generation unit 15 zero current detection unit 16 PWM output control unit 21 zero current indirect detection unit 31 zero current period measurement unit A1, B1 to B5 Current sensor C1 Sense capacitor Cc Coupling capacitor Co Output capacitor Comp1 Comparator D1, D2 Driver FF1 SR flip-flop La Input side inductor Lb Output side inductor Q1 Switching element Q2 Synchronous rectification element R1 Resistor Ro Output load Vi Input DC power supply

Claims (3)

An input side inductor connected between an input DC power supply and a first terminal of a coupling capacitor, an output side inductor connected between a second terminal of the coupling capacitor and ground, and the coupling capacitor A synchronous rectification SEPIC circuit comprising: a switching element connected between the first terminal and the ground; and a synchronous rectification element connected between the second terminal of the coupling capacitor and an output terminal. A DC-DC converter comprising
the inductances of the input side inductor and the output side inductor are set to the same value;
a zero current detection unit that detects the end of the regenerative current flowing through the input side inductor and the output side inductor and outputs a zero current detection signal;
an output control unit that turns off the synchronous rectifier element in response to the zero-current detection signal from the point in time when the end of the regenerative current is detected to the start of the next switching period ;
The input side inductor or the output side inductor is used as a detection inductor, and the zero current detection unit is provided in parallel with the detection inductor to indirectly detect the voltage generated across the DC resistance component of the detection inductor. A DC-DC converter characterized by a zero-current indirect detection unit that detects the end of the regenerative current flowing through the detection inductor . The zero current detection unit includes an RC circuit including a resistor and a sense capacitor connected in parallel with the detection inductor, and the value obtained by multiplying the resistance value of the resistor and the capacitance of the sense capacitor is the The inductance of the detection inductor is set to be equal to the value obtained by dividing the resistance value of the DC resistance component of the detection inductor, and the voltage across the sense capacitor terminates the regenerative current flowing through the detection inductor. The DC-DC converter according to claim 1 , characterized in that it detects. a zero-current period measurement unit that measures a zero-current period during which the output control unit turns off the synchronous rectification element, and reduces switching frequencies of the switching element and the synchronous rectification element as the zero-current period becomes longer. 3. The DC-DC converter according to claim 1 or 2, characterized in that:

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